The present invention relates to a heater for vehicles. More specifically, the present invention pertains to a heater that has a rotor and viscous fluid in its housing and generates heat by the rotor rotation shearing the viscous fluid.
A heater using the drive force of a vehicle engine is described, for example, in a U.S. Pat. No. 4,974,778. The heater will now be described with reference to FIG. 7.
A conventional heater 70 has a housing including a heating chamber 72 and a ring-shaped space 73. The ring-shaped space 73 is formed adjacent to the outer side of the heating chamber 72. Further, a reservoir 74 is partitioned parallel to the heating chamber 72. A middle wall 75 separates the heating chamber 72 and the reservoir 74. A drive shaft 76 is supported to rotate in the housing. A rotor 77, which rotates integrally with the drive shaft 76 in the heating chamber, is rigidly attached to one end of the drive shaft 76, and a pulley 78 is fixed to the other end of the drive shaft 76. The pulley 78 is rotated by the engine drive force by way of a belt.
A certain amount of viscous fluid 79 is put in the heating chamber 72 and the reservoir 74, occupying a clearance 82 between the peripheral surface 80 of the rotor 77 and an inner wall 81 of the heating chamber 72. A supply passage 83 and a return passage 84 are formed in the middle wall 75. The supply passage 83 supplies the fluid from the reservoir 74 to the heating chamber 72, and the return passage 84 returns the fluid back to the reservoir 74. The opening degree of the supply passage 83 is adjusted by a lever 86, which is controlled by a bimetallic plate spring 85. This adjusts the heat generation capacity of the heater 70. When the temperature of a coolant 88 has not reached a required level for heating, the bimetallic plate spring 85 maintains the supply passage 83 open. This permits the supply of viscous fluid 79 from the reservoir 74 to the heating chamber 72.
When the drive force of the engine is transmitted to the pulley 78, the rotor 77 rotates with the drive shaft 76 in the heating chamber 72. This shears the viscous fluid 79 between the rotor periphery 80 and the inner wall 81 and generates heat. The heat is transferred to the coolant 88 flowing in the ring-shaped space 73, through partitions 87 and supplied to a heat exchanger of a heating apparatus for vehicles. The fluid is returned to the reservoir by centrifugal force via the return passage 84.
The return of the viscous fluid from the heating chamber to the reservoir is stopped when the rotor stops with the engine. This leaves a substantial amount of viscous fluid adhering to the rotor in the heating chamber. When the rotor is restarted in this state, a load resulting from the adhered fluid is applied to the engine through the rotor and the belt. This may cause the drive belt to slip. As a result, ride comfort is deteriorated, and noise and wear of the heater parts are more likely to occur. Accordingly, one technical challenge has been to lower the load when starting the rotation of the rotor.